— Notes on Colour — the so-called artists’ primaries

a typical naive illustration of paint mixing — These are typical of illustrations that purport to explain colour mixing.

Colour myths

There is no such thing as painters’ primaries. When people say the primary colour are red, yellow and blue, they usually mean one of four things, all of which are misleading:

Some people use red and blue as the colour names for magenta and cyan when they are talking about the subtractive primaries.
Some painters refer to the colours they use when they are mixing paint as if they obeyed different laws of perception from colours produced in any other way.
Some commentators² have a mystical belief in fundamental, unmixed colours which they fail to connect to evidence about human perception (or mixing paints).
Most commonly, people refer arbitrarily to a particular set of paint colours which they have found to produce a usefully large range of hues This could be any one of many sets of primaries that work well enough to be accepted. We accept them, given the complexities of subtractive mixing and the forgiving nature of human vision.

There are clear physical reasons why colour mixing is not going to be consistent from one type of paint to another. Perceptually identical colours will mix in different ways if their pigments have different absorbtion spectra—if they are a metameric pair.

Observations

Sometimes people use the term pigment primaries to refer to painters’ primaries. This is misleading because the cyan, magenta and yellow pigments in printers inks, for example, are clearly effective as subtractive primaries. It’s a nice little irony that the illustrations on this page were not produced by mixing the illustrated colours—they were originally printed in a book using the CMYK system. If you examine of the book closely enough, the illustrations themselves show you how the colours aren’t mixing as the illustrations claim!
As I type this note I can see the cyan stain in my hand from a tube of gouache. I had to open it. The tube was clearly labelled process cyan but the colour swatch on the tube was just as clearly blue, not cyan! The stain on my hand confirms that the paint is indeed cyan. I am fascinated by the contortions that people go through to maintain the myth that red, yellow and blue are the subtractive primaries.
Before the current three primaries fad became entrenched, painters would comfortably use four basic colours for mixing. These would have been called red, yellow, green and blue, but the red would have been more magenta and the blue more cyan than the red and blue used in these notes.
Even if they were consistent, there would be no reason to call paint-mixing primaries the primary colours because this only confuses our understanding of every other use of colour. Basing the colour wheel on these false primaries produces a misleading notion of what complementary colours are. The concept of complementary colours is only useful when it’s based on an understanding of human perception, not on an understanding of the quirks of paint mixing.
Sometimes people use the term artists’ primaries to refer to painters’ primaries, as if sculptors, print makers, photographers, installation artists, artists in digital media and performance artists were all not artists.